Boiler repair

ABSTRACT

Boiler tube repair apparatus includes elongated guide rail structure for securing to a boiler tube panel adjacent a desired cut region, and three tool assemblies for mounting on the guide rail structure. Each tool assembly includes carriage structure with guide structure for engaging the guide rail structure and support structure on which a tube machining tool is mounted and that defines a tool movement axis dedicated to and coordinated with that tool. Each machining tool includes a drive motor, a manual motor control, a drive shaft and a machining member such as a cutter disc or head.

This is a division of application Ser. No. 07/131202, filed Dec. 10,1987 and now U.S. Pat. No. 06/916302 filed Oct. 7, 1986 and now U.S.Pat. No. 4739688.

This invention relate to repair of boilers and the like, and moreparticularly to methods and apparatus for repairing a panel of defectiveboiler tubes.

Steam generation systems in modern power plants include boilers withbanks of steel (and other alloys) tubes that extend vertically fordistances frequently in excess of one hundred feet Such tubes have outerdiameters of up to three inches and more with wall thickness of up toabout one half inch, adjacent tubes being connected together with metalmembranes Such tube walls deteriorate due to corrosion and the like, andpanel portions of such boiler tube walls require periodic replacement.Typically, repair of such defective boiler tube panels has involvedremoval of the tube panel by flame cutting, finishing (smoothing andbeveling) the ends of the cut tubes, and then inserting and welding inplace a replacement panel of tubes--an expensive and time consumingprocess. Prior attempts to saw through such tube walls have not beenparticularly successful as the saw, due to the size and materials of theboiler tubes, cannot be held with sufficient stability to provide astraight cut line by advancing the saw along the line to be cut eitherby hand or on an appropriate support.

In accordance with one aspect of the invention, a boiler tube panelrepair system includes elongated guide rail structure for securing to aboiler tube panel adJacent a desired cut region, and a plurality ofprocessing tool assemblies for mounting on the guide rail structure,each processing tool assembly including a support carriage with guidestructure for engaging the guide rail structure. A first tool assemblyincludes secured to its support carriage that has a plunge cutting axisextending transversely to the guide rail structure; and a cutting toolmounted on the carriage that includes a drive motor, a manual motorcontrol, a drive shaft and a tube cutter disc mounted on the drive shaftfor rotation about an -axis parallel to the plunge cutting axis. Thisfirst, processing tool assembly is adapted..-to sever....a panel oftubes to be replaced from adjacent boiler tube structure and providesstraight and precise cutting of a panel of boiler tubes with resultingsmooth aligned tube end surfaces.

A second processing tool assembly for cutting boiler wall membraneportions adjacent the cut tube end surfaces includes a similar carriagewith support structure secured to its carriage that has a membranecutting axis extending parallel to the guide rail structure; a cuttingtool mounted on the main pivot that includes a drive motor, a manualmotor control, a drive shaft, and a tube cutter disc mounted on thedrive shaft for rotation about an axis perpendicular to the membranecutting axis, the second tool providing exposed circumferential tube endsurfaces that may be quickly and accurately prepped (e.g., beveled) forwelding of replacement boiler tubes in place of the removed panel ofboiler tubes.

A third processing tool assembly for prepping the exposed tube endsurfaces has similar carriage structure with reference axis definingstructure fixedly secured to its carriage, the reference axis extendingperpendicular to the guide rail structure; and a tube end prepping toolmounted for swiveling movement about the reference axis including acutter head and a drive motor for rotating the cutter head about an axisparallel to the reference axis for end prepping exposed tube endsurfaces for welding of a replacement boiler tube panel to the originalboiler tubes.

In accordance with another aspect of the invention, there is provided aprocess for repairing a panel of defective boiler tubes that includesthe steps of mounting elongated guide rail structure on a boiler tubepanel adjacent the panel of tubes to be repaired, sequentially disposinga series of tool assemblies on the guide rail structure, each toolassembly including a tube cutting member and carriage structure forengaging the guide rail structure, and then moving the tube cutting toolmember relative to its carriage to machine portions of the boiler tubepanel. The tube cutting processes and apparatus of the invention enablerapid and efficient repair of defective boiler tube sections and thelike including machining steps such as cutting and accurate end preppingfor receiving a replacement boiler tube panel that is then welded inplace.

In a particular embodiment, the elongated guide rail structure issecured to the boiler tube panel by a plurality of rail supports, eachrail support includes an alignment projection whose end is adapted to bepositioned immediately adjacent the desired cut line on the boiler tubepanel, and a body portion which is adapted to be secured to a boilertube surface and which carries rail fastening means. Each supportcarriage includes a frame assembly on which first and second pairs ofspaced guide wheels are mounted. Each guide wheel has a V-groove thatengages a correspondingly shaped edge surface of the guide rail.Preferably, the first and second tool assemblies each include brakestructure for engagement with the guide rail structure to lOck thesupport carriage relative to the boiler tube wall during cutting oftubes or membranes, each brake structure including a brake shoe and anoperating member, the shoe being movable by the operating member betweena disengaged position and an engaged position in which the shoe isengaged with the surface of the guide rail to lock its cutting toolassembly in place on the rail.

In preferred embodiments, the first tool assembly includes secondarypivot structure secured to the support carriage, plunge cut linkstructure mounted on the secondary pivot structure that includes a firstlink connected to the cutting tool and a second link connected betweenthe first link and the secondary pivot axis for manually rotating thecutting tool about the main pivot axis in plunge cutting action througha panel of tubes adjacent the guide rail structure, manually releasablelatch structure for holding the cutting tool in raised position; andstabilizing structure on the support carriage for storing the cuttingtool assembly in upright position when not in use. In a particularembodiment, the stabilizing structure includes an arm that projectslaterally from the longitudinal frame member beneath the cutting tool,the plunge cut link structure includes a coupling which is slidinglyreceived on the second link, and the manually releasable latch structurelatches the plunge cut coupling and first link together.

In preferred embodiments, the third tool assembly includes an end preptool assembly that includes a drive motor and a cutter head that ismounted for rotation about an axis parallel to and offset from the drivemotor axis. The cutter head includes a plurality of cutter blade insertsand a body that has a plurality of recesses for receiving the cutterblade inserts, each recess having configured sidewalls which permit thecutter blade inserts to be inserted only in proper orientation and alsoenhance the security attachment of the blade inserts. A pilot projectioncoaxial with the axis of rotation of the cutter head is fixed forrotation with the cutter head and adapted to be received within theinner diameter of the tube whose end surface is to be prepped.Preferably, the axis of the cutter head is disposed outwardly of itsdrive motor and such that end prepping of tubes in a corner or at theend of a panel is facilitated. The tool drive motor is adapted to drivethe cutter head in rotation at a speed of at least about 1,000 rpm, andin a particular embodiment, the drive motor is an air motor that drivesthe cutter head at about 15,000 rpm.

When used in the track system, this end prep tool is fixedly mounted oncarriage structure that includes reference axis defining structure thathas a reference axis extending transversely to the guide rail structure,and the end prep tool is mounted on the reference axis definingstructure for swiveling movement about the reference axis. A drivearrangement coupled between the reference axis defining structure andthe end prep tool includes a rack and pinion gear arrangement for movingthe cutter head along a path parallel to the reference axis to end prepa boiler tube, such as to provide a suitable bevel (e.g., 37 1/2°) onthat tube for subsequent welding. The reference axis defining structureincludes a shaft member and the gear arrangement is fixedly clamped tothe shaft while allowing swiveling movement of the end prep tool aboutthe reference axis and movement of the end prep tool along a pathparallel to the reference axis.

Other features and advantages of the invention will be seen as thefollowing description of a particular embodiment progresses, inconjunction with the drawings, in which:

FIG. 1 is a perspective view of components of a boiler tube panel repairsystem in accordance with the invention;

FIG. 2 is a side elevational view of the elongated guide rail componentof the boiler tube repair system of FIG. 1;

FIG. 3 is a side elevational view, similar to FIG. 2, showing tubecutting apparatus mounted on the guide rail;

FIG. 4 is a sectional view taken along the line 4--4 of FIG. 3;

FIG. 5 is a top elevational view of the cutting tool system of FIG. 3;

FIG. 6 is a diagrammatic view of the cutting tool system from the sideopposite that of FIG. 5;

FIG. 7 is a side elevational view, similar to FIG. 2, showing membranecutting apparatus mounted on the guide rail;

FIG. 8 is a sectional view taken along the line 8--8 of FIG. 7;

FIG. 9 is a top elevational view of the membrane cutting system of FIG.7;

FIG. 10 is an end elevational view, similar to FIGS. 4 and 8, showingtube end beveling apparatus mounted on the guide rail;

FIG. 11 is a bottom view of the tube beveling head employed in theassembly shown in FIG. 10;

FIG. 12 is a front elevational view of the carbide insert employed inthe beveling head of FIG. 11;

FIG. 13 is a top view of the carbide insert employed shown in FIG. 12;and

FIG. 14 is a perspective view of the tube beveling system shown in FIGS.10 and 11.

DESCRIPTION OF PARTICULAR EMBODIMENT

Shown in FIG. 1 is a bank of boiler tubes 10 that includes a rectangularpanel of tubes that is to be replaced. Mounted on the bank of tubes 10is elongated guide rail 12. rail 12 includes a steel member about sixfeet in length and about 1 3/4 inch in width and about one quarter inchin thickness, and aluminum reinforcing plate 14 (FIG. 4) that is bondedto the rear surface of guide rail 12. Apertures 16 are spaced along thelength of rail 12 at five inch intervals. Rail support members 18 arewelded to the outer surface of spaced tubes as indicated in FIGS. 1 and2. Each rail support 18 includes an alignment projection 20 whose end ispositioned immediately adjacent the desired cut line 22 on the boilertube panel; and a body portion 24 which is welded to a boiler tubesurface and which carries an upstanding stud 26. Rail 12 is secured onsupports 18 by nuts 28.

Mounted on rail 12 is tube cutting tool assembly 30 that includescarriage 32 which has longitudinal frame member 34, forward transverseframe member 36 on which a first pair of spaced guide wheels 38 aremounted for rotation, and rear transverse frame member 40 on which asecond pair of spaced guide wheels 42 are mounted. Each guide wheel 38,42 has a V groove that engages a correspondingly shaped guide surface 44of guide rail 12. Secured to rear transverse frame member 40 is mainpivot bracket 46 which defines a pivot axis 47 perpendicular to rail 12and on which support 48 is pivotably mounted. Secured to support 48 iscutting tool 50 that includes motor housing 52, drive gear housing 54,drive shaft 56 on which cutter disc 58 is secured, and protective dischousing 60. Tool 50 also has handle 62 which carries manually operablecontrol switch 64. Power is supplied to motor 52 (a 5,000 rpm threehorsepower motor) by heavy duty high amperage power supply cord 66.

With reference to FIGS. 3-6, secured to forward transverse carriageframe member 36 is plunge cut pivot bracket 70 that carries pivot socket72 in which is received plunge cut lever 74 for rotational movementabout a pivot axis 71 that is defined by pivot bracket 70 and isparallel to axis 47. Slidingly received on lever arm 74 is plunge cutcoupling 76 to which is rotatably attached support link 78 that issecured to the upper surface of gear housing 54. Plunge cut handle 80 isattached to coupling 76. Recess 82 in plunge cut lever 74 cooperateswith a latch mechanism that includes a spring biased latch member housedin coupling 76 that latches the cutting tool assembly 30 in raisedposition (as shown in FIG. 6) and is operable by latch actuator 88. Thelatch member is released by depression of latch actuator 88 to disengagethe latch member from lever recess 82 and allow coupling 76 to slidealong lever 74.

Mounted on longitudinal frame member 34 of the tool carriage is brakeassembly 92 that includes brake shoe 94 and operating member 96, shoe 94being movable by operating member 96 between a raised position (shown inFIG. 6) and a lower position (shown in FIG. 5) in which shoe 94 isengaged with the surface of guide rail 12 to lock the cutting toolassembly 30 in place on rail 12. Stand member 98 extends laterally fromlongitudinal frame member 34 and cooperates with guide wheels 38 toprovide a stable support for the tube cutting tool assembly 30 on thefloor or other surface when not in use.

The system includes a second cutting tool assembly 110 for cuttingmembranes 108 between adjacent tubes 10. Details of that membranecutting assembly 110 may be seen with reference to FIGS. 7-9. Membranecutting assembly 110 includes carriage 32' on which two pair of spacedguide wheels 38', 42' are mounted. Each guide wheel 38', 42' (similar toguide wheels 38, 42 of tube cutting assembly 30) has a V groove 111 thatengages a correspondingly shaped guide surface 44 of guide rail 12 asindicated in FIG. 8. Secured to carriage 32' is pivot bracket 46' thathas a pivot axis 112 parallel to rail 12 and on which tool support 48'is pivotable mounted. Cutting tool 114 is secured to support 48' andincludes three horsepower 5,000 rpm motor 116, drive gear housing 118,drive shaft structure 120 on which cutter disc 122 is secured, and discguard 124. Tool 114 also has handle 126 which carries manually operablecontrol switch 128 and operating handle 130 which is secured to drivegear housing 118 by bracket 132 and bolt 134. Power is supplied to motor116 through heavy duty high amperage power supply cord 136.

Mounted on carriage 32' is brake assembly 92' that includes brake shoe94' and operating member 96', shoe 94' being movable by handle 96'between a raised position (shown in FIG. 8) and a lower position whereshoe 94' engages guide rail 12 to lock the cutting tool assembly 110 inplace on rail 12.

A third tool assembly 150 (for beveling tube ends) is shown in FIGS.10-14. Beveling tool assembly 150 is adapted to cooperate with rail 12similar to the other system tool assemblies 30 and 110. Tool assembly150 includes support carriage 32" which carries two pairs of spacedguide wheels 38", 42", each of which has a corresponding V-groove 111'that engages the correspondingly shaped guide surface 44 of guide rail12. Tool assembly 150 includes elongated cylindrical rod 152 that issecured to carriage 32' by bolts 154 and nuts 156 and defines a pivotaxis perpendicular to rail 12. Adjustably secured on rod 152 by clampactuator 158 is stop member 160.

Tool support frame 170 includes rack gear 172 fixed between supportmembers 174, 176, rack gear teeth 178 being in engagement with teeth 180of pinion gear 182 that is mounted on gear support 169. Also mounted onsupport frame 170 is 1.8 horsepower 90 psi, 15 000 rpm air motor unit184 and cutter head 188 is coupled in offset relation through drive gear186 such that drive motor 184 is located generally between the axis ofcutter head 188 and the reference axis of shaft 152. Gear support 168 isfixed on shaft 152 by clamp frame 190 and bolt 192 such that thebeveling tool motor unit 184, its gear drive 186 and offset cutter head188 are allowed to swivel about the axis of shaft 152. The motor unit184 and its support frame 170 are biased upwardly relative to clampframe 190 by spring 194 to the position shown in FIG. 10. Secured topinion gear 182 is actuating arm 196 that rotates pinion gear 182 todrive the engaged rack gear 172 downwardly, carrying motor support framemembers 174, 176 and the air motor 184 with cutter head 188 downwardly.As the air motor and cutter head assembly is free to swivel about theaxis of shaft 152, it can be aligned with a tube 10 whose end surface200 is to be beveled.

With reference to FIGS. 10-13, cutter head 188 has cylindrical body 202with threaded through bore 204 that receives the threaded end 206 ofshaft 207 of gear unit 186 at one end and threaded shaft portion 208 ofpilot 210 at the other end. Pilot 210 has cylindrical body 212 ofdiameter corresponding to the inner diameter of tubes 10 whose endsurfaces 200 are to be beveled and in which are formed axially extendinggrooves or recesses 214. Also formed in body 202 are recesses 218 thatreceive carbide cutter blade inserts 220. Each recess 218 has a basesurface 222 that extends parallel to a radius of body 202 and sidewallsurfaces 224 that are inclined outwardly at an angle of 10°. A carbidecutting insert 220 is secured in each recess 218 with fastener 226 sothat its cutting edge 228 is inclined at a 37 1/2° bevel angle. Eachcarbide blade insert 220 is of parallelogram configuration as indicatedin FIG. 12 and has sidewalls 230, each of which is at a 10° angle toinsert face 232 as indicated in FIG. 13, and through hole 234 forreceiving fastener 226.

In repair of a defective portion of a boiler tube wall, the plungecutting tool assembly 30 is used to sever the boiler tubes, horizontaland vertical cuts being made through the boiler tubes on four sides sothat the rectangular panel of tubes to be replaced may be removed, thehorizontal cuts exposing tube ends 220. The plunge cutting tool and itscarriage 32 is then removed from rail 12, and the carriage 32' ofmembrane cutting assembly 110 is positioned on rail 12 and tool 114 isoperated to cut membranes 108 adjacent those tube ends 220. Aftermembranes 108 have been cut, assembly 110 is removed from rail 12 andcarriage 32" of the beveler unit 150 is mounted on the guide rail 14 andcutter head 188 is swiveled into alignment with tube ends 220 andoperated to form bevels 254 for welding.

In system use, as indicated in FIGS. 1 and 2, an operator 100 (onvertically adjustable scaffolding--not shown) locates a desired cut line22, welds a first rail support 18A to a boiler tube with the end of itsalignment tab 20 immediately adjacent the cut line 22. Rail 12 is thenmounted on the stud 26A of the fixed support 18A and secured with nut28A. A second rail support 18B is then similarly- loosely secured torail 12 with securing nut 28B and its alignment tab 20B similarlypositioned adjacent cutting line 22. The body of weld tab 18B is thentack welded in place on the boiler tube and the nuts 28A, 28B tightenedon their respective coupling studs 26 to secure rail 12 parallel to, butoffset from cut line 22. Rail 12 provides a fixed stable reference forthe carriages 32, 32', 32" of the plunge, membrane and bevel cut tools.

The plunge cutting tool assembly 30 is mounted on rail 12 by slidingguide wheels 38, 42 onto the rail edge surfaces 44, as indicated in FIG.1, there being sliding clearance between transverse frame members 36, 40and studs 26. In that position, cutter disc 58 is located in alignmentwith cut line 22. The tool carriage is then locked in place with brakeassembly 92. Motor 50 is then energized with control switch 62 and theoperator 100 releases latch 88 and urges handle 80 towards rail 12,rotating plunge cut lever 74 forward about the axis of pivot bracket 70(as indicated in FIG. 1 and by line 102 in FIG. 6). That rotationalmovement of plunge cut lever 74 causes coupling 76 to slide along rod 74along a path 104 (about the plunge cut axis of main pivot 46). As plungecut lever 34 is rotated forwardly towards the boiler tubes, cutter disc58 is moved along arc 106 into and cuts through the boiler tubes 10 andtheir interconnecting membranes 108 in a plunge cutting stroke (to aposition indicated by dotted line 58' in FIG. 6). After the boiler tubeplunge cut stroke has been completed, the operator 100 raises handle 80,rotating plunge cut lever 74 in the opposite direction to raise thecutting tool 50, and optionally latch the tool in raised position Afterthe cutter disc 58 is clear of the boiler tubes 10, the operatorreleases the brake 92 and advances the cutting tool assembly along rail12 to reposition the assembly 30 for the next plunge cutting stroke.

Contiguous plunge cutting strokes are successively repeated to producethe cut line 22 as generally indicated in FIG. 1 (the cut line beingstraight but appearing to vary due to the location of the boiler tubes10 in the boiler wall). After the series of contiguous plunge cuts havebeen made along the length of the rail, the cutter disk 58 may beenergized and the tool rotated into the position 56', and the toolassembly 30 is then slid along the rail to provide a smooth linear cutsurface 200 of the tubes 10 and membranes 108.

After similar horizontal and vertical cuts are made through the boilertubes on four sides (the vertical cuts being through membranes 108), theresulting rectangular panel of tubes to be replaced is removed.

The plunge cut unit is then removed from rail 12 and the carriage 32' ofthe membrane cutting tool assembly 110 is positioned on the rail so thatit utilizes the same basic fixed support and reference. Disc 122 of toolassembly 110 is aligned with one edge of a tube 10 and the tool assemblyis locked in place by brake 92'. Motor 116 is energized, and the tool114 is pivoted about its membrane cutting pivot axis 112 to make cuts250 in membranes 108 at ends 200 of the immediately adjacent cut boilertubes 10. Any remaining intermediate membrane portion 252 may then besnapped off with pliers or a similar device so that the entirecircumferential end surface 200 is exposed for beveling prior to weldingof the replacement panel tube.

This beveling is accomplished with the beveler tool 150 shown in FIGS.10 and 14. After the membrane cutting tool assembly 110 is removed fromrail 12, tool carriage 32" is inserted on rail 12 as indicated in FIGS.10 and 14

The beveler tool 150 is then swiveled about the axis of support post 152to align cutter head 188 with the end 200 of a tube 10 to be beveled sothat the pilot 210 may be inserted into the inner diameter of the tube10. Actuation of throttle control 166 energizes air motor 184 to rotatecutter head 188 at 15,000 rpm and depression of operating handle 196,moves head 188 down, inserting pilot 210 into tube to stabilize thecutter head 188. The high speed (15,000 RPM) rotation of carbide inserts220 provides rapid effective cutting of end surface 200 to provide 371/2° bevel surface 254, the depth of the bevel being controlled by stop160. After the bevel is completed, the assembly is returned to itsinitial position by spring 194.

In another beveler tool embodiment, the beveler tool is hand-held andsimilarly includes a high speed cutter head 188 with pilot 210 which isinserted into the ID of the tube to be end prepped, and drive motor 166.Such a hand held tool may carry an adjustable projecting stop that isaligned with rail 12 or other reference to control the depth of thebeveling action.

The system provides accurate and efficient cutting of tubes of adefective boiler tube panel of tubes and subsequent end prepping withresulting aligned end-prepped tube surfaces prepared for insertion of areplacement panel that is then welded in place.

While a particular embodiment of the invention has been shown anddescribed, various modifications thereof will be apparent to thoseskilled in the art, and therefore it is not intended that the inventionbe limited to the disclosed embodiment, or to details thereof, anddepartures may be made therefrom within the spirit and scope of theinvention.

What is claimed is:
 1. A boiler repair system comprisingelongated guiderail structure for securing to a boiler tube panel adjacent a region tobe replaced, a first tool assembly for mounting on said guide railstructure, said first tool assembly including first carriage structurewith guide structure for engaging said guide rail structure and enablingsaid first tool assembly to be stably moved along said guide railstructure and, first support structure secured to said first carriagestructure and defining a plunge cutting axis extending transversely tosaid guide rail structure, a first cutting tool mounted on said firstsupport structure for movement about said plunge cutting axis in plungecutting action to cut through a series of boiler tubes, said firstcutting tool including a tube cutter disc disposed for rotation about anaxis parallel to said plunge cutting axis and a first motor for drivingsaid tube cutter disc in rotation, and a second tool assembly formounting on said guide rail structure, said second tool assemblyincluding second carriage structure with guide structure for engagingsaid guide rail structure so that said second tool assembly may bestably moved along said guide rail structure, second support structuresecured to said second carriage structure and defining a membranecutting axis extending parallel to said guide rail structure, and asecond cutting tool mounted on said second support structure thatincludes a membrane cutter disc disposed for rotation about an axisperpendicular to said membrane cutting axis, and a second motor fordriving said membrane cutter disc in rotation for cutting membranesbetween boiler tubes cut by said first cutting tool; and a third toolassembly for mounting on said guide rail structure, said third toolassembly including third carriage structure with guide structure forengaging said guide rail structure so that said third tool assembly maybe stably moved along said guide rail structure, third support structuresecured to said third carriage structure and defining a reference axisextending perpendicularly to said guide rail structure, said third toolassembly including a tube end prepping tool mounted on said thirdsupport structure for swiveling movement about said reference axis andincluding a cutter head mounted for rotation about an axis parallel tosaid reference axis, and a drive motor for driving said cutter head inrotation for end prepping boiler tubes cut by said first cutting tool.2. The system of claim 1 wherein each of said first and second toolassemblies each includes brake means for engagement with said guide railstructure to lock each of their respective carriage structures relativeto said panel of boiler tubes during boiler tube and membrane cuttingoperations respectively.
 3. The system of claim 2 wherein each saidbrake means includes a brake shoe and an operating member, said shoebeing movable by said operating member between a disengaged position andan engaged position in which said shoe is engaged with the surface ofsaid guide rail to lock said cutting tool assembly in place on saidrail.
 4. The system of claim 1 wherein said drive motor of said thirdtool assembly is adapted to drive said cutter head in rotation at aspeed of at least one thousand rpm.
 5. The system of claim 1 wherein theaxis of said cutter head is disposed such that said drive motor islocated generally between said cutter head axis and said reference axis.6. The system of claim 1 wherein said cutter head of said third toolassembly includes a plurality of cutter blade inserts, a body and aplurality of recesses in said body for receiving said cutter bladeinserts, each said recess having configured sidewalls so that saidcutter blade inserts can be inserted only in proper orientation.
 7. Thesystem of claim 1 wherein said cutter head of said third tool assemblyincludes a pilot projection coaxial with the axis of rotation of saidcutter head, said pilot projection being fixed for rotation with saidcutter head and adapted to be received within the inner diameter of thetube whose end surface is to be prepped
 8. The system of claim 1 whereinsaid elongated guide rail structure is secured to said boiler tube panelby a plurality of rail supports, each said rail support including analignment projection whose end is adapted to be positioned immediatelyadjacent the desired cut line on the boiler tube panel, and a bodyportion which is adapted to be secured to a boiler tube surface andwhich carries upstanding rail fastening means.
 9. The system of claim 1wherein each said carriage structure includes frame structure on whichtwo pairs of spaced guide wheels are mounted.
 10. The system of claim 9wherein each said guide wheel has a groove that engages acorrespondingly shaped guide surface of said guide rail.
 11. The systemof claim 10 wherein said cutter head of said third tool assemblyincludes a plurality of cutter blade inserts, a body and a plurality ofrecesses in said body for receiving said cutter blade inserts, each saidrecess having configured sidewalls so that said cutter blade inserts canbe inserted only in proper orientation; said cutter head of said thirdtool assembly includes a pilot projection coaxial with the axis ofrotation of said cutter head, said pilot projection being fixed forrotation with said cutter head and adapted to be received within theinner diameter of the tube whose end surface is to be prepped.
 12. Thesystem of claim 11 wherein said drive motor of said third tool assemblyis adapted to drive said cutter head in rotation at a speed of at leastone thousand rpm.
 13. The system of claim 12 and further including adrive arrangement that includes a first component fixed with respect tosaid reference axis structure and a second component secured to said endprep tool and cooperating with said first component to move said endprep tool along path parallel to said reference axis.
 14. The system ofclaim 1 wherein said first tool assembly includes secondary pivotstructure secured to said first carriage structure, plunge cut linkstructure mounted on said secondary pivot structure that includes afirst link connected to said first cutting tool and a second linkconnected between said first link and said secondary pivot structure formanually rotating said first cutting tool about said plunge cutting axisin plunge cutting action through a panel of tubes adjacent said guiderail structure.
 15. The system of claim 14 and further includingmanually releasable latch structure cooperating with said plunge cutlink structure for holding said first cutting tool in raised position,andstabilizing structure on said first support carriage for storing saidfirst tool assembly in upright position when not i- use.
 16. The systemof claim 15 wherein said elongated guide rail structure is secured tosaid boiler tube panel by a plurality of rail supports, each said railsupport including an alignment projection whose end is adapted to bepositioned immediately adjacent the desired cut line on the boiler tubepanel, and a body portion which is adapted to be secured to a boilertube surface and which carries upstanding rail fastening means.
 17. Aboiler tube machining process comprising the steps ofmounting elongatedguide rail structure on a boiler tube panel adjacent a desired repairregion, disposing a tube cutting tool assembly on said guide railstructure, said tube cutting tool assembly including a tube cutting discdisposed parallel to said guide rail structure, fixedly positioning saidtube cutting tool assembly at a first location on said guide railstructure, moving said tube cutting disc about a fixed pivot axis thatextends transversely to said guide rail structure to make a first plungecut through the panel of boiler tubes, moving said tube cutting toolassembly along said guide rail structure from said first location to asecond location on said guide rail structure while said tube cuttingdisc is spaced from said boiler tube panel, moving said tube cuttingdisc about a fixed pivot axis that extends transversely to said guiderail structure at said second location to make a second plunge cutthrough the panel of b oiler tubes in alignment with and as an extensionof said first plunge cut, and repeating the steps of moving said tubecutting tool assembly along said guide rail assembly from location tolocation while said tube cutting disc is spaced from said boiler tubepanel and moving said tube cutting disc at each such location about afixed pivot axis t make a series of plunge cuts, the resulting series ofplunge cuts being aligned with said first and second plunge cuts andproviding an elongated cut through the panel of boiler tubes.
 18. Theprocess of claim 17 wherein said tube cutting tool assembly includesprimary pivot structure on which said tube cutting tool is mounted forrotation about said fixed pivot axis, and secondary pivot structure onwhich plunge cut link structure is mounted, and said step of moving thetube cutting tool is accomplished by operating said plunge cut linkstructure to rotate said cutting disc about said fixed pivot axis. 19.The process of claim 18 wherein said plunge cut link structure includesa first link connected to said cutting tool and a second link connectedbetween said first link and said secondary pivot structure, and saidstep of moving said tube cutting tool about said fixed pivot axis isaccomplished by manually rotating said second link about said secondarypivot to rotate said tube cutting tool about said fixed pivot axis inplunge cutting action through a panel of tubes adjacent said guide railstructure.
 20. A boiler tube machining process comprising the stepsofmounting elongated guide rail structure on a boiler tube paneladjacent a desired repair region, disposing a tube cutting tool assemblyon said guide rail structure, said tube cutting tool assembly includinga tube cutting disc disposed parallel to said guide rail structure,fixedly positioning said tube cutting tool assembly on said guide railstructure, moving said tube cutting disc about a fixed pivot axis inplunge cutting action to cut through the panel of boiler tubes, removingsaid tube cutting tool assembly from said guide rail structure,disposing a membrane cutting tool assembly on said guide rail structure,said membrane cutting tool assembly including a membrane cutting discdisposed perpendicularly to said guide rail structure, fixedlypositioning said membrane cutting tool assembly on said guide rialstructure, and moving said membrane cutting disc about a fixed pivotaxis in membrane cutting action to cut through a boiler tube membraneimmediately adjacent the end surfaces of boiler tubes cut by said tubecutting tool assembly.
 21. The process of claim 20 wherein said tubecutting and membrane cutting tool assemblies each further includesreleasable brake structure, and said step of fixedly positioning saidtube cutting and membrane cutting tool assemblies on the guide railstructure each includes the step of operating its said brake structure.